This phase II, multi-national, double-blind, placebo-controlled, parallel group, 16 week study will assess the safety and potential of CDP571 to prevent disease flare while allowing steroid withdrawal in steroid-dependent patients with Crohn's disease following and IV dose of 20 mg/kg and then, 8 weeks later, 10 mg/kg of CDP571. Subjects will be montiored throughout for safety. Primary efficacy endpoint is the percentatge of patients who have not experienced a disease flare and who no longer require steroid therapy at Week 10.